Fluorosilicone hydraulic fluids

ABSTRACT

R AND R&#39;&#39; ARE ARALKYL RADICALS CONTAINING NO MORE THAN 3 ALIPHATIC CARBON ATOMS ARE DISCLOSED AS IMPROVED HYDRAULIC FLUIDS. EXEMPLARY OF SUCH A FLUID IS 3,3,3-TRIFLUOROPROPYLMETHYLPOLYSILOXANE HAVING A VISCOSITY OF 40 CS. AT 77*F. WHICH IS ENDBLOCKED WITH 2-PHENYLETHYLDIMETHYLSILOXY UNITS.   IN WHICH   R-SI(-CH3)2-O-(SI(-CH3)(-CH2-CH2-RF)-O)N-SI(-CH3)2-R&#39;&#39;   FLUOROSILICONE FLUIDS OF THE FORMULA

United States Patent 3,660,453 FLUOROSHLICONE HYDRAULIC FLUIDS Eugene D. Groenhof and Harry M. Schiefer, Midland,

Mich., assignors to Dow Corning Corporation, Midland, Mich.

No Drawing. Continuation-impart of application Ser. No. 564,742, July 13, 1966. This application Jan. 10, 1969, Ser. No. 790,443

Int. Cl. CtWt 7/02 US. Cl. 260-448.2 R 4 Claims ABSTRACT OF THE DISCLOSURE Fluorosilicone fluids of the formula ii...i is

in which This application is a continuation-in-part of application Ser. No. 564,742, filed July 13, 1966, and now abandoned.

This application relates to hydraulic fluids which exhibit improved performance over the known fluorosilicone fluids such as trimethylsiloxy-endblocked 3,3,3-trifluoropropylmethylpolysiloxane.

For use in high altitude aircraft, hydraulic fluids must have a very low pour point, i.e., remain fluid at very low temperatures. In addition, these fluids must have a certain low degree of compressibility to avoid waste of energy in power transmission. The fluids must also have lubricity, be stable at high temperatures and be relative- 1y inflammable. Known fluorosilicone fluids, such as trimethylsiloxane-endblocked 3,3,3 trifluoropropylmethylpolysiloxane, possess many of these desirable properties, but are restricted to use in less severe environments because of a relatively high pour point.

The hydraulic fluids of this invention have less compressability, a higher ignition temperature, and generally equal or improved lubricity when compared with the above 'known organopolysiloxanes. The fluids of this invention are also particularly susceptible to having their lubricity improved by means of the addition of a small amount of an organophosphorus additive such as dioctyl phosphite or tricresyl phosphate to form fluids having outstanding lubricity. The organophosphorus additives are also easily dissolved in the fluids.

Accordingly, it is an object of the invention to provide an improved fluorosilicone fluid.

Another object of the invention is to modify the structure of known fluorosilicone fluids to obtain improved low temperature properties while retaining the other desirable characteristics.

These and other objects of the invention will be apparent to one skilled in the art upon consideration of the following specification and appended claims.

Patented May 2, 1972 ice More particularly, the invention relates to a fluid consisting essentially of at least one organopolysiloxane of the formula t t 1 i RSiO-Si0 -SiR' 6H llilHz J $11 zRr n in which R and R are aralkyl radicals containing no more than 3 aliphatic carbon atoms,

R, is a perfluoroalkyl radical of no more than 8 carbon atoms, and

n is so selected to yield a polymer having a viscosity at 77 F. of 20 to 500 cs.

The unexpected discovery of this invention is that the addition of aralkyl-containing groups to the endblocks of fluorosilicone fluids results in a marked improvement in several properties, rendering the fluid more suitable for use as a lubricating oil or a hydraulic fluid, particularly at high temperatures. It is further unexpected that these fluids have very low temperature pour points despite the addition of the aralkyl groups.

R and R can each be an aralkyl radical such as benzyl or Z-phenylpropyl; 2-phenylethyl, 3-phenylpropyl, 2-tolylethyl and the like. R, can be any perfluoroalkyl radicals as defined above, e.g. trifluoromethyl, perfluoroisobutyl, prefluorohex'yl, and perfluorooctyl.

The organopolysiloxanes used herein are easily prepared through the known techniques of organosilicon chemistry, such as that disclosed in US. Pat. 2,961,425. The viscosity of the product is easily controlled by controlling the concentration of endblocking-groups present during the preparative process, which usually consists of reacting a cyclic trimer with disiloxane endblocking material. An alternative method involves addition of arylcontaining vinyl compounds to SiH-containing fluorosilicone fluids. For example, the reaction of vinyltoluene with dimethylhydrogensiloxy-endblocked 3,3,3-trifluoropropylmethylpolysiloxane in the presence of chloroplatinic acid produces a fluid of the invention. Generally n has a value of from 3 to 70.

The following example is illustrative only and should not be construed as limiting the invention, which is properly delineated in the appended claims.

EXAMPLE 1 The following fluids within the scope of the invention were tested:

Fluid A: 3,3,3 trifluoropropylmethylpolysiloxane having a viscosity at 77 F. of 40.4 cs. and having Z-phenylethyldimethylsiloxane endblocks.

Fluid B: 3,3,3 trifluoropropylmethylpolysiloxane having a viscosity at 77 F. of 79.4 es. and having 2- tolylethyldimethylsiloxane endblocks.

\Fluid C: 3,3,3-trifluoropropylmethylpolysiloxane having a viscosity at 77 F. of 46.4 cs. and having 2-phenylpropyldimethylsiloxane endblocks.

For purposes of comparison the following fluids were also tested:

Fluid D: 3,3,3-trifluoropropylmethylpolysiloxane having a viscosity at 77 F. of 52.8 es. and having endblocks consisting of 67 mol percent of diphenylmethylsiloxane and 33 mol percent of phenyldimethylsiloxane.

Fluid E: 3,3,3-trifluoropropylmethylpolysiloxane having a viscosity at 77 F. of 46.7 cs. and having endblocks consisting of 45 mol percent of diphenylmethylsiloxane and 55 mol percent of phenyldimethylsiloxane.

F. of 100 cs. in which Fluid A B c D E F G P0urp0i t,F 94 -87 90 -70 Speeiflegravity( C.) 1.169 1.171 1.150 1.170 1.185 1. 251 1.220 Compressability at 20,000 psi. (percent) 6. 68 6. 57 6.45 6.13 6. 6.45 7. Auto ignition temperature F.) 020 076 010 940 983 350 (ASTM D-286):

Shell 4-ball test 400 F. 1,020 r.p.in., hr.

20 kg, scar diam. (mm) 0.67 0-79 .86 0.72 0.76 0.80 0.80 Same 4-ball test with 1% tricresyl phosphate 0. 57 0.35 0. 34 0. 45 0.50 0.35 0. 67

Mineral when Subjected to these Same tests, Sh WS R and R are aralkyl radicals containing no more than 3 a compressibility of approximately 6.1%, an Auto-ignialiphatic carbon t tion temperature of about 700 F. and a pour point of 20 R is a perfluoroalkyl radical of no more than 8 carbon about -30 F. atoms; and

It is apparent from the data, that fluids A, B and C n is so selected to yield a polymer having a viscosity having pour point of approximately 90 F. are uniqueat 77 F. of 20 to 500 cs. ly suitable as hydraulic fluids for use in severe environ- 2. The fluid of claim 1 wherein R and R are 2- ments. The relatively low degree of compressibility has 25 phenylpropyl radicals and R, is a trifluoromethyl radical. been retained and the fluid does not readily burn. The 3. The fluid of claim 1 wherein R and .R' are 2-phenylfluid which contains the phosphate additive exhibits signiethyl radicals and R, is a trifluoromethyl radical. ficant increase in lubricity. 4. The fluid of claim 1 wherein R and R are 2-tolyl- It is also apparent that the fluids (A, B and C) of ethyl radicals and R; is a trifluoromethyl radical. the invention possess superior properties to known fluoro- 0 silicone fluids, such as Fluids D, E, F and G. These fluids, References Cited tested for comparison, do not exhibit the desirable low UNITED STATES PATENTS tem erature r0 erties and would not be suitable for use in cgrtain g l environment 2,961,425 11/1960 Plerce at al. 260-4482 X 0:- 3,006,878 10/1961 Talcott 260-4482 X It 1s withln the scope of the invention to provide a 0-) s 3,267,031 8/l966 Buehler 260448.2 X method of transmittin power comprising applying pies- 3 317 429 5/1967 C k d l 26 sure to the fluids of the invention which are confined in e a a at a 0*4482 X a hydraulic system. Other reasonable modification and TOBIAS ELEVOWPrimary Examiner variation are w1thm the scope of the lnventlon. 40

That which is claimed is:

1. A fluid having a pour point of approximately -90 F. consisting essentially of at least one organopolysiloxane of the formula W. F. W. BELLAMY, Assistant Examiner US. Cl. X.R. 25278, 77, 

